1. Field of the Invention
The present invention relates to a paper web feed unit used in a rotary press and equipped with a paper web traveling tension controller, and more particularly to a paper web feed unit which is used in a rotary press and in which a paper web having a width double that of paper used in a press unit is longitudinally cut, by use of cutting means, into two cut paper webs having substantially the same width; only one of the cut paper webs is passed through an angle bar section; and the traveling tension of each cut paper web is controlled by use of a paper web traveling tension controller.
2. Description of the Related Art
Japanese Patent Publication (kokoku) No. 51-007083 discloses a conventional rotary press in which a paper web is longitudinally cut, by use of cutting means, into two cut paper webs having substantially the same width; the first cut paper web is fed to a first press unit via an angle bar section; and the second cut paper web is fed directly to a second press unit without passing through the angle bar section.
In the rotary press, while the first cut paper web passes through the angle bar section, the traveling path thereof is transferred such that the first cut paper web is fed to the first press unit in a state in which the center line thereof is aligned with the center line of the second cut paper web that is fed to the second press unit.
Further, a traveling tension controller as disclosed in "Newspaper Printing Handbook," pp. 111-112, published by Japanese Newspapers Association, Apr. 10, 1997 (.sctn.3 "Newspaper Offset Rotary Press," (2) Infeed Tension) has generally been used to control the traveling tension of a paper web fed to a press unit.
The traveling tension controller is used to stabilize the traveling tension of a paper web fed to a press unit and is designed to control the traveling tension of the paper web at a location before the press unit by use of an infeed roller and a dancer roller.
FIG. 4 shows such a traveling tension controller combined with the above-described rotary press.
In FIG. 4, a paper web WO' having a width double that of paper used in an unillustrated press unit of a rotary press is taken out of a paper roll W' and is longitudinally cut, by use of cutting means C', into two cut paper webs having substantially the same width. Subsequently, a first cut paper web W1' of a single width is passed through an angle bar section D', so that the center line of the first cut paper web W1' coincides with the center line of a second cut paper web W2' of a single width.
For the cut paper webs W1' and W2', paper web traveling tension controllers T1 and T2 are provided in order to enable the cut paper webs W1' and W2' to be fed to respective press units while their traveling tensions are controlled independently.
The paper web traveling tension controller T1 (T2) includes a dancer roller 42a (42b) connected to a fluid cylinder 41a (41b). The dancer roller 42a (42b) applies a pushing pressure to the cut paper web W1' (W2') due to projection of the piston rod of the fluid cylinder 41a (41b), and moves in accordance with variation in the traveling tension of the cut paper web W1' (W2').
Further, an infeed roller 43a (43b) driven by a drive source 45a (45b) is provided upstream of the dancer roller 42a (42b); and a sensor 44a (44b) for detecting the position of the dancer roller 42a (42b) is attached to the fulcrum of a support arm of the dancer roller 42a (42b). The drive source 45a (45b) receives a detection signal from the sensor 44a (44b) and changes the circumferential speed of the infeed roller 43a (43b) in order to control the amount of the paper web fed to the dancer roller 42a (42b) such that the dancer roller 42a (42b) is always located at a neutral position (ordinary position) in the slack/tension direction of the cut paper web W1' (W2').
Thus, a stable traveling tension is applied to the cut paper web W1' (W2') fed to the press unit.
The above-described conventional techniques involve various drawbacks, as described below.
In the rotary press disclosed in Japanese Patent Publication No. 51-007083, no paper web traveling tension controller is provided in a paper threading path extending from the cutting means of the paper web feed unit where a paper web taken out of the paper roll is cut to the press unit. Therefore, when the traveling tension of the cut paper web changes (for example, decreases) due to resistance of rollers for supporting and guiding the cut paper web and a paper dragging operation performed downstream of the press unit, the traveling cut paper web slacks and meanders, resulting in paper breakage or other problems. On the contrary, when the traveling tension of the cut paper web increases, wrinkles are generated in the traveling cut paper web, also resulting in paper breakage or other problems.
In order to overcome the above-mentioned drawbacks, as shown in FIG. 4, the above-described paper web traveling tension controller is combined with the rotary press disclosed in Japanese Patent Publication No. 51-007083. However, the rotary press shown in FIG. 4 has a drawback in that a difference in traveling state is produced between the cut paper web W1'--which travels from the cutting means C' to the infeed roller 43a along a paper threading path containing an angle bar section D' which generates extremely high friction resistance--and the cut paper web W2'--which travels from the cutting means C' to the infeed roller 43b along a paper threading path containing no angle bar section.
That is, when the rotary press is started and the supply of cut paper webs W1' and W2' to the respective press units is started at the same paper speed by means of paper drag rollers (not shown) provided downstream of the press units, the dancer rollers 42a and 42b of the paper web traveling tension controllers T1 and T2 start to move in the tensing direction of the cut paper webs W1' and W2' (rightward in FIG. 4) as the traveling tensions of the cut paper webs W1' and W2' increase. However, due to the action of the infeed rollers 43a and 43b, the dancer rollers 42a and 42b are controlled to return to the respective neutral positions (ordinary positions).
In the above-described case, since the cut paper web W1' is subjected to the high friction resistance of the angle bar section D', the cut paper web W1' elastically deforms and stretches in a region between the angle bar section D' and the infeed roller 43a, and thus travels slightly slower than the cut paper web W2' in a region between the cutting means C' and the angle bar section D'. As a result, in the region between the cutting means C' and the angle bar section D', a difference in traveling tension is produced between the cut paper web W1' and the cut paper web W2', with the result that the cut paper web W1' slacks.
However, when the rotary press is operated continuously, the difference between the traveling tension of the cut paper web W1' in the region between the cutting means C' and the angle bar section D' and the traveling tension of the cut paper web W1' in the region between the angle bar section D' and the infeed roller 43a converges to a constant value determined from the friction resistance between the angle bar section D' and the cut paper web W1', and in this state, the cut paper web W1' starts to travel at substantially the same speed as the cut paper web W2'. Therefore, no significant problems occur.
However, when low speed operation and stoppage of the rotary press are performed repeatedly many times within a short period of time; for example, in a work step in which an operator attaches a printing plate onto a plate cylinder, the difference between the traveling tension of the cut paper web W1' in the region between the cutting means C' and the angle bar section D' and that in the region between the angle bar section D' and the infeed roller 43a does not converge to a constant value, even though the rotation of the infeed roller 43a is controlled such that the dancer roller 42a returns to the neutral (ordinary) position. In this case, the cut paper web 1' travels intermittently, with the result that the amount of slack in the cut paper web W1' at a region downstream of the cutting means C' increases.
By contrast, unlike the cut paper web W1', the cut paper web W2' does not slack, with the result that at a location where the cutting means C' cuts the paper web W0', the cut paper web W2' comes into a slightly pulled state as compared to the cut paper web W1'.
Therefore, a cut line formed by the cutting means C' meanders or skews slightly.
When the cut paper web W1' and the cut paper web W2' are caused to travel simultaneously upon a speed increasing operation after start of printing, a large difference in traveling tension is suddenly produced between the cut paper web W1' and the cut paper web W2' in a region immediately after the cutting means C', with the result that one or both of the cut paper webs W1' and W2' is broken, and a slacked portion of the cut paper web W1' is caught by the cutting means C' or other rollers, which stops the operation.
Accordingly, there has been a strong desire for a paper web traveling tension controller which can be used in the structure in which a paper web taken out of a paper roll is longitudinally cut, by means of cutting means, into two cut paper webs having substantially the same width, and one of cut paper webs is passed through an angle bar section in order to transfer the traveling path of the cut paper web; which prevents sudden generation of a large difference in traveling tension between the two cut paper webs which would otherwise be generated in a region downstream of the cutting means when the rotary press is operated intermittently at slow speed; and which does not cause any problem during continuous operation of the rotary press.